All of patents, patent applications, patent publications, scientific articles and the like, which will hereinafter be cited or identified in the present application, will hereby be incorporated by references in their entirety in order to describe more fully the state of the art, to which the present invention pertains.
In a SOI MOSFET, it is well known that On-current (current at ON) changes depending on its operation history by a history effect. Therefore, it is necessary to know a dynamic I-V characteristic as well as a DC I-V characteristic for the SOI MOSFET.
Conventionally, a pulse measurement method as shown in FIG. 1 has been used for measuring the dynamic I-V characteristic. In FIG. 1, the source of MOSFET 105 is grounded, the drain is connected to a power source through inductive load (L1) 121, and also to oscilloscope 120 through a capacitive element (C1). In addition, pulse generator 119 is connected to the gate.
If a square wave is inputted into MOSFET 105 from pulse generator 119, a current flowing in inductive load (L1) 121 changes according to a change of drain current of MOSFET 105, thereby resulting in change of a drain voltage. The change of the drain voltage is measured by oscilloscope 120. If a characteristic of inductive load (L1) 121 is known, a change of the drain current can be obtained from the change of the drain voltage. A relation between amplitude of the inputted square wave and the drain current constitutes the I-V characteristic during pulse input. This has been disclosed in, for example, IEEE Electron Device Letters, Vol. 16, No. 4, p145, 1995.
Other than the above measurement method, there exists a method called a drain conductance method as shown in FIG. 2. In this method, an impedance analyzer is connected to the source and the drain, while applying a DC voltage to the gate, and a differential conductance gD between the source and the drain is measured by applying an AC signal. If the differential conductance gD is integrated by the drain voltage, the I-V characteristic at a frequency of the AC signal can be obtained. This has been disclosed in, for example, IEEE Journal of Solid-State Circuit, Vol. 27, No. 8, p1186, 1992.
For designing a circuit of SOI MOSFET, SOI-enabled SPICE (circuit simulator) parameters, for example, BSIM SOI is used. For extracting the parameters, a value of a DC I-V measurement is used. This has been disclosed in, for example, BSIM PD2.1 MOSFET MODEL Users Manual BSIM Research Group 1999.
Voltage is measured with an oscilloscope in the pulse measurement method. However, since the voltage dissolution of the oscilloscope is low compared with that of a DC current meter and a DC voltage meter, an accuracy of the measured voltage is low. In addition, since various frequency signals are included in the square signal, it is impossible to obtain the I-V characteristic at a specified frequency.
The drain conductance method has a higher accuracy than the pulse measurement method because of the use of impedance analyzer. However, since the measurement is conducted at a constant gate voltage, the I-V characteristic is different from that of a practical operation of the MOSFET. Then, there exists a problem that the dynamic I-V characteristic at the practical operation of the MOSFET can not be obtained.
Furthermore, since the dynamic I-V characteristic at the practical MOSFET operation is not known, a parameter fitting for the dynamic I-V characteristic is not implemented at SOI-enabled SPICE parameter extraction.